Check the OS name for variants
Check the OS name for variants

If an OS supports variants, unless --force-variant is specified a valid
variant must be passed.

Signed-off-by: Guido Trotter <f62ca4d5358bdaeef0e50e57f9f7e231de63727e@google.com>
Reviewed-by: Olivier Tharan <0947fcc917eb1d3c89ad818beb61e3b2c3cf3bba@google.com>

ganeti/ganeti,ganeti-github-testing/ganeti-test-1,grnet/snf-ganeti,yiannist/ganeti,bitemyapp/ganeti,leshchevds/ganeti,onponomarev/ganeti,yiannist/ganeti,apyrgio/ganeti,andir/ganeti,dimara/ganeti,bitemyapp/ganeti,dimara/ganeti,mbakke/ganeti,apyrgio/ganeti,ganeti-github-testing/ganeti-test-1,ganeti/ganeti,andir/ganeti,mbakke/ganeti,grnet/snf-ganeti,yiannist/ganeti,apyrgio/snf-ganeti,onponomarev/ganeti,ganeti/ganeti,leshchevds/ganeti,mbakke/ganeti,apyrgio/snf-ganeti,leshchevds/ganeti,andir/ganeti